Bio-irrigation by two important polychaete species on the Belgian Part of the North Sea

Type:

Master Thesis subject (30 ECTS)

programme:

EMBC+

The sea floor is an important component of the coastal marine ecosystem, as it is the environment where large amounts of organic material are deposited after the annual phytoplankton bloom. Mineralisation of this organic matter results in fluxes of nutrients to the water column, where they fuel the next phytoplankton bloom. Mineralisation is most efficient in the presence of oxygen. Oxygen concentrations in coastal sediments are largely affected by the activities of sediment inhabiting fauna.
Previous research showed that the Sand mason (Lanice conchilega), a tube-building polychaete, irrigates the sediment with overlying water, thereby increasing the oxygen content of the sediment and stimulating the mineralization of organic matter. A similarly looking polychaete species (Owenia fusiformis) lives in more rigid tubes, and is more tolerant to sludge disposal. While it is highly abundant on certain areas of the Belgian Part of the North Sea, there is no information on its effects on the sedimentary environment.
Here, we will investigate whether Owenia fusiformis should be considered as important as Lanice conchilega. By experimental research, we will compare the bio-irrigation rates of both species, and test whether these are density and context (sediment type) dependent. This is highly relevant, as human activities (aggregate extraction, installation of offshore wind farms) at sea result in a fining of the sediments. Consequently, Lanice conchilega is now occurring in high densities where it has been absent before, and the suitable habitat for Owenia fusiformis can be increasing as well. This thesis therefore contributes to an ongoing project aiming at the understanding of the functional consequences at the ecosystem scale, from local anthropogenic activities.